1. Field of the Invention
The present invention relates to a plasma display apparatus, and more particularly, to a plasma display apparatus in which the construction of a terminal of the plasma display apparatus is improved, thereby preventing damage to electrodes and securing the flame retardation property.
2. Discussion of the Related Art
Generally, in a plasma display apparatus, a barrier rib formed between a front panel and a rear panel both of which are made of soda-lime glass forms one unit cell. Each cell is filled with a main discharge gas such as neon (Ne), helium (He) or a mixed gas (Ne+He) of Ne and He, and an inert gas containing a small amount of xenon. If the inert gas is discharged with a high frequency voltage, vacuum ultraviolet rays are generated. Phosphors formed between the barrier ribs are light-emitted to display an image.
FIG. 1 is a perspective view illustrating the construction of a plasma display panel (PDP) according to a related art. As shown in FIG. 1, the PDP includes a front panel 10A in which a plurality of sustain electrode pairs having scan electrodes Y and sustain electrodes Z are arranged on front glass 1A serving as the display surface on which the images are displayed, and a rear panel 10B in which a plurality of address electrodes X disposed to cross the plurality of the sustain electrode pairs is arranged on rear glass 1B serving as the rear surface. At this time, the front panel 10A and the rear panel 10B are parallel to each other with a predetermined distance therebetween.
The front panel 10A includes the scan electrodes Y and the sustain electrodes Z, which perform discharge against the other in a mutual manner and maintain emission of cells, in one discharge cell. That is, each of the scan electrodes Y has a transparent electrode 2Y made of a transparent ITO material, and a bus electrode 3Y made of a metal material. Further, each of the sustain electrodes Z has a transparent electrode 2Z made of a transparent ITO material, and a bus electrode 3Z made of a metal material. The scan electrodes Y and the sustain electrodes Z are covered with an upper dielectric layer 4 for limiting a discharge current and providing insulation among the electrode pairs. A protection layer 5 on which magnesium oxide (MgO) is deposited in order to facilitate a discharge condition is formed on the entire surface of the upper dielectric layer 4.
Barrier ribs 7 of a stripe type (or a well type), for forming a plurality of discharge spaces, i.e., discharge cells, are arranged parallel to each other in the rear panel 10B. Further, a plurality of address electrodes X that perform an address discharge to generate vacuum ultraviolet rays are disposed parallel to the barrier ribs 7. R, G and B phosphors 8 that emit visible rays for image display upon address discharge are coated on a top surface of the rear panel 10B. A low dielectric layer 9 for protecting the address electrodes X is formed between the address electrodes X and the phosphors 8.
In the related art PDP constructed above, a frame in which scan, sustain and address driving units are formed, and a terminal for supplying a predetermined signal from each driving unit to the PDP, as the constituent elements of the plasma display apparatus, are formed at the rear surface.
FIG. 2 is a plan view illustrating the construction of a plasma display apparatus according to the related art. FIG. 3 is a partial cross-sectional view of the plasma display apparatus taken along line A-A′ in FIG. 2.
Referring to FIGS. 2 and 3, the plasma display apparatus is divided into a panel display unit D1 serving as the PDP, and a panel terminal D2 (area/structure surrounding the display unit D1).
The panel display unit D1 has the same structure as described in FIG. 1. The panel display unit D1 includes a front panel 10A, a rear panel 10B, and a seal material 12 that seals the front panel 10A and the rear panel 10B to form a discharge cell. The front panel 10A includes transparent electrodes 2Y, 2Z (2) constituting scan electrodes or sustain electrodes that are formed on front glass 1A in a parallel way, metal bus electrodes 3Y, 3Z (3) formed at the edges on the transparent electrodes 2Y, 2Z (2), a metal bus electrode pad 11 that extends from the metal bus electrodes 3Y, 3Z (3) up to the panel terminal D2, and an upper dielectric layer 4 and a protection film 5 that are sequentially formed on the front glass 1A to cover the transparent electrodes 2, the metal bus electrode 3 and the metal bus electrode pad 11. The rear panel 10B includes address electrodes X formed on the rear glass 1B to cross the scan electrodes or the sustain electrodes, and a lower dielectric layer laminated on a rear glass to cover the address electrodes X.
The panel terminal D2 includes the metal bus electrode pad 11 that is formed on the front glass 1A to extend from the panel display unit D1, and a film type element 14 that is connected to the metal bus electrode pad 11 and applies a driving signal controlled in a printed circuit board (PCB). At this time, the metal bus electrode pad 11 and the film type element 14 are adhered using an anisotropic conductive film (hereinafter, referred to as “ACF”) 16. The ACF 16 has a film form in which metal-coated epoxy or conductive particles such as metal particles are dispersed. It serves to electrically connect the metal bus electrode 3 and the film type element 14.
In the panel terminal D2 in which the film type element 14 and the metal bus electrode pad 11 are adhered using the anisotropic conductive film 16, the metal bus electrode pad 11 made of silver (Ag) is exposed to external air. Thus, when a PDP is driven, there is a problem in that the electrodes are damaged due to reaction with external environment, such as temperature, moisture, corrosive gas and/or conductive alien substance, i.e., migration.
This migration phenomenon can be expressed into the following Chemical Formulae (1) to (5).Ag++e−→Ag  (1)O2+2H2O+4e−→4OH−  (2)2H2O+2e−→4OH−  (3)Ag→Ag++e−  (4)H2O→½O2+2H++2e−  (5)
First, if neighboring two electrodes (e.g., between Y and Z electrodes) include silver (Ag) and a voltage difference is generated between the pads 11 of these two electrodes, the pads 11 of the neighboring two electrodes become the cathode and the anode, respectively. Thus, a positive ion (Ag+) of silver is eluted in the anode, as in Chemical Formula (4), and then moves to the cathode under dissolved oxygen. Accordingly, the reduction reaction is generated in the cathode, as in Formula (1), and silver is thus precipitated on the cathode. Chemical Formulae (2) and (3) indicate the rate-deciding step of deciding the generation rate of migration, Chemical Formula (2) indicates the reduction reaction of dissolved oxygen, and Chemical Formula (3) indicates electrolysis and hydrogen creation reaction.
If an application voltage rises and a voltage difference between the pads 11 of the two electrodes becomes high, the current is increased and the generation of migration is accelerated that much. In other words, if the application voltage rises, the current of the cathode is increased due to Chemical Formulae (2) and (3) being the initial reaction of the cathode, so that elution reaction current of silver in the anode increases. That is, if electrolysis occurs between the pads 11 of the two neighboring electrodes, as in Chemical Formula (5), and oxygen is generated accordingly, Ag+ of silver existing in the anode moves to the cathode, and the reaction such as Chemical Formulae (2) and (3) is thus generated on a surface of the cathode. Ag+ is combined with OH−, and is then dispersed in collide form of AgOH, Ag, Ag2O compound on the surface of the cathode. Consequently, if a voltage difference occurs between the pads 11 of the two electrodes, surface discoloration is generated and open electrodes are generated in each of the neighboring two pads 11 or shortage is generated between the two pads 11.
As such, in order to prevent electrode discoloration and electrode short due to the reaction of moisture, in the related art, ultraviolet hardening resin being epoxy acrylate based resin having a high hardening strength and good wetproof property is coated on the panel terminal D2.
Further, there is a problem of abnormal discharge and erroneous discharge, wherein a cell where a discharge cell must be turned on is turned off or a cell where a discharge cell must be turned off is turned on because of heat generated due to the load of various causes, such as voltage load or switching load of a switching element, when a PDP is driven. Further, if the load becomes high and much heat is generated, fire can be generated in the panel terminal including the film type element in which much heat is generated, among the constituent elements of the PDP. Accordingly, this creates a problem in that the function of the PDP is fully lost and the PDP can be rendered inoperative.
This problem, i.e., the problem of lowered picture quality such as erroneous discharge and abnormal discharge due to the generation of heat can be improved by controlling a voltage applied to the panel in the conventional circuit unit or a voltage waveform. As far as the heat actually generated when the PDP is driven, however, there is no alternate heatproof means except for radiation of heat using a heatproof plate attached to the rear side of the PDP or a heat sink formed on a driving circuit substrate. Thus, if a heat radiation characteristic is not good, there is a problem in that the above-described display terminal loses its function of the PDP since it is vulnerable to fire and malfunction.